Carrier for electrophotography

ABSTRACT

The present invention is a carrier for electrophotography in which a surface of at least a core material is coated with a resin, in which the coating resin contains a fluorine modified silicone resin and an aminosilane coupling agent, and in which the carrier charges a toner negatively. Consequently, a carrier with a high durability and a long lifetime for electrophotography is provided, in which the charge amount does not decrease at high temperature or high humidity nor extremely increase at low temperature or low humidity, in which a deterioration of a developing agent caused by stripping of a coating layer is prevented, and in which a deterioration caused by formation of spent toner of a toner is not caused.

TECHNICAL FIELD

The present invention relates to a carrier for electrophotography thatis used for a copier, a laser printer, a plain paper fax, a color PPC, acolor laser printer, a color fax, or a multifunctional machine of these.

BACKGROUND ART

Conventional electrophotographic processes generally use a method inwhich an electrostatic latent image is formed on a photosensitive memberor an electrostatic recording member by using various means, a toner isadhered to this electrostatic latent image, and then the electrostaticlatent image is developed.

In this development, carrier particles called “carriers” are mixed withtoner particles so as to charge each other triboelectrically, and thuspositive or negative electric charge of an appropriate amount isimparted to the toner. Carriers are classified roughly into coatedcarriers that have a coating layer on their surface and uncoatedcarriers that do not have a coating layer on their surface. Coatedcarriers are superior to uncoated carriers in light of, for example, thelifetime of the developing agent.

Among the various properties required for a coated carrier that areparticularly important are a property of imparting an appropriate charge(the amount and the distribution of electric charge) to a toner, aproperty of keeping the appropriate charge on the toner for a longperiod of time, and for this purpose, shock resistance, abrasionresistance, a property of sufficiently inhibiting formation of spenttoner, and a property of preventing a change in the charge on the tonerby resisting environmental changes such as humidity or temperature.Various coated carriers have been proposed.

For the purpose of providing a long-lived coated carrier, JP S61-80163A,for example, proposes a technique in which a surface of a carrier corematerial is coated with a resin such as a copolymer of a vinyl monomerand fluorinated alkyl (meth)acrylate containing nitrogen, or a copolymerof fluorinated alkyl (meth)acrylate and a vinyl monomer containingnitrogen. JP H2-24670A, for example, proposes use of a copolymer of avinyl monomer and fluorinated alkyl (meth)acrylate containing nitrogen,and a copolymer of fluorinated alkyl (meth)acrylate and a vinyl monomer.Furthermore, JP H6-11908A, for example, proposes a solvent-solublefluorine-containing polymer having an imide bond. According to these, acoated carrier with a relatively long lifetime is obtained by coating asurface of the carrier core material with a copolymer of anitrogen-containing monomer and a fluorinated monomer, or asolvent-soluble fluorine-containing polymer having an imide bond.However, the coated carrier may not withstand use for a long period oftime when these copolymer resins are used. This is because the adhesivestrength of the coating resins at an adhesive interface with the carrieris poor due to an influence of a low surface energy of the fluorinegroup, and because sufficient shock resistance cannot be obtained due tothe insufficient strength of the resins as a coating agent. Furthermore,in order to charge the toner negatively, the amount of added fluorinatedmonomer needs to be kept small, and thus it was not possible to obtain acharged member having a sufficiently low surface energy while impartinga sufficient charge to the toner. Consequently, over a long period ofuse, formation of spent toner of the toner or an external additive tothe charged member cannot be inhibited sufficiently. Thus the chargecharacteristics deteriorate with the time of usage, so that problemssuch as image fog or density non-uniformities are caused. “Formation ofspent toner” refers to the phenomenon that, for example, a toner, anexternal additive and/or a colorant are/is firmly adhered or fused on asurface of a charged member due to heat generated by mechanicalcollision or friction, for example, between particles or between aparticle and a developing device.

Furthermore, JP H7-325426A, for example, proposes a long-lived coatedcarrier in which a fluororesin is mixed and used together with a resinconventionally used as a coating material of a carrier forelectrophotography (for example, an acrylic resin, an epoxy resin,styrene, a styrene-acrylic resin, or a silicone resin) as a binder or aprimer, so that the poor adhesive strength of the fluororesin asdescribed above is reinforced.

However, when the fluororesin, which is more negative in thetriboelectric series, and the binder resin, which is more positive inthe triboelectric series, are mixed to coat the surface of the carriercore material as described above, there is a difference in thecharacteristics such as the melting point of these resins. Thus auniform resin coating layer is difficult to obtain, there is a broaddistribution of charge amounts, and image defects such as fog or tonerscattering are caused, and the transfer efficiency may be lowered.

Furthermore, fluororesins have the characteristic of moving to theoutermost layer of the resin coating layers when mixed and used withanother resin, and thus the charge amount decreases significantly for anegatively charged toner. In addition, when the coating layer isstripped by a long period of use, the fluororesin is stripped first, andthe binder resin appears at the outer layer with the time of usage, andthus a change in, for example, charge characteristics becomessignificant.

A carrier coated with a silicone resin coating layer has been proposedconventionally as a carrier having a relatively low surface energy.Although formation of spent toner of a toner tends to occur less if thecoating layer is made of a silicone resin due to its relatively lowsurface energy, the effect is not sufficient. Furthermore, due to itslow surface energy and high insulation, the charge amount is extremelydifficult to increase, and image defects such as fog or toner scatteringtend to occur.

Use of a silane coupling agent has been proposed in order to improve theadhesiveness of a resin coating layer to address image deterioration(for example, insufficient image density or image fog defects) causedwhen the resin coating layer on a surface of a carrier is stripped orlost due to, for example, collision between carriers or friction betweena development box and a carrier due to stirring (JP S60-19156A).Although the adhesiveness of the coating layer is improved, there is aproblem that toner scattering or image fog is caused due to fluctuationin the charge amount under various environmental conditions.

For the purpose of improving the adhesiveness between a carrier corematerial and a silicone resin, JP S62-121463A, for example, illustratesa carrier in which a coating layer made of a silicone resin is providedon a surface of a carrier core material treated with a silane couplingagent. However, the outermost surface of this carrier is not providedwith a component of an aminosilane coupling agent containing aneffective amino group, and thus the carrier cannot impart charge to anegatively charged toner sufficiently, and scattering is caused at thetime of printing. Thus, a satisfactory carrier still is not obtained.

Furthermore, Japanese Patent No. 2744790, for example, proposes acarrier that is coated with a silicone resin containing an aminosilanecoupling agent, for the purpose of preventing a decrease in the chargeamount on a toner in a highly humid atmosphere and of improvingdurability of a developing agent, when used in combination with a tonerwith its components limited. A decrease of the charge amount throughoutits lifetime can be improved by the limitation of the toner componentsand the effect of the aminosilane coupling agent. However, the formationof spent toner of the toner is not inhibited sufficiently, although ittends to occur less.

Recently, JP H5-134467A, for example, has proposed a resin layercontaining an aminosilane coupling agent that is double-coated and inwhich the components or additives in the resin of the intermediate andthe outermost layer are different.

Furthermore, JP H5-204189A illustrates a carrier characterized in that adensity gradient of, for example, a silane coupling agent is provided ina thickness direction of a silicone resin layer. The carrier does nothave uniform constituents in the carrier resin layers, and thus thesilicone resin-coated carrier particularly changes over time when leftstanding, and a difference in hardening appears between the outermostlayer and the intermediate layer of the resin layers. Therefore, asignificant difference in charge characteristics appears between tonersfrom the initial stage of production and toners after a certain periodof time, the charge amount decreases at high humidity when a conductivematerial is added, and carrier resistance changes significantly if theresin layers are stripped or lost at the time of printing. Thus, in thefinal evaluation, it cannot be said to have durability.

Furthermore, JP H7-104522A proposes a resin-coated carrier for adeveloping agent of electrophotography characterized in that a carriercore material has a resin coating layer made of a silicone resin or amodified silicone resin containing an aminosilane coupling agent, inthat the aminosilane coupling agent is present in the coating resin in arange of 6 to 25 weight percents, and in that the equivalent weight ofamino groups in the aminosilane coupling agent ranges from 163 to 235.In this technique, a base resin of the resin coating layer containingthe aminosilane coupling agent is a silicone resin or a modifiedsilicone resin. Examples of the modified silicone resin include variousmodified silicone resins such as an alkyd resin, a polyester resin, anepoxy resin, a polyurethane resin, and an acrylic resin. These baseresins cannot inhibit sufficiently formation of spent toner of a toneror an external additive to charged members over a long period of use,and thus their charge characteristics deteriorate with the time ofusage, so that problems such as image fog or density non-uniformitiesare caused.

For the purpose of obtaining a negatively charged carrier (a positivelycharged developing agent) whose triboelectrical charge characteristicsare excellent and in which stripping tends not to occur, JP S60-213961Aproposes a carrier in which a coating layer containing a terminalperfluoro alkylsilane coupling agent in a silicon varnish is formed on acore surface. However, the silicon varnish and the terminal perfluoroalkylsilane coupling agent are difficult to apply uniformly, and thusthe coating layer tends to be nonuniform, such as generated when afluororesin and a binder resin are mixed and used together as describedabove. Consequently, there is a broad distribution of charge amounts,and image defects such as fog or toner scattering are caused.

Japanese Patent No. 2801507 proposes a carrier in which for a positivelycharged toner, a fluorine-substituted alkyl group is introduced to asilicone resin of a coating layer. Furthermore, as a carrier in whichdevelopment properties in a high speed process are high and whoseproperties are not deteriorated over a long period of time, JP2002-23429A proposes a coated carrier containing conductive carbon and acrosslinked fluorine modified silicone resin. This carrier takesadvantage of excellent charge characteristics of the silicone resin,imparts characteristics such as sliding properties, stripping propertiesdue to the fluorine-substituted alkyl group, and water-repellingproperties, tends not to cause abrasion, stripping, or cracks, and canprevent formation of spent toner. However, abrasion, stripping, orcracks are not prevented satisfactorily. Furthermore, although anappropriate charge amount can be obtained for a positively chargedtoner, the charge amount is too small when a negatively charged toner isused, so that a large amount of oppositely charged toner (positivelycharged toner) is generated. Consequently, fog or toner scattering isaggravated, and thus the carrier may not withstand use. Furthermore, thetransfer efficiency may be lowered.

In other words, a carrier having a resin coating layer containing onlyfluororesin can be used only for a positively charged toner due to theposition in the triboelectric series, and the adhesive strength of thecoating resin at an adhesive interface with the carrier is poor.Furthermore, the carrier cannot obtain sufficient shock-resistance dueto the insufficient strength of the resin as a coating agent, and thusit may not withstand use for a long period of time.

When a fluororesin and another resin are mixed and used, a uniform resincoating layer is difficult to obtain, there is a broad distribution ofcharge amounts, and image defects such as fog or toner scattering arecaused. Furthermore, fluororesins have the characteristic of moving tothe outermost layer of the resin coating layers when mixed and used withanother resin, and thus the charge amount decreases extremely for anegatively charged toner. In addition, when the coating layer isstripped by a long period of use, the fluororesin is stripped first, andthe binder resin appears at the outer layer with the time of usage. Thusa change in, for example, charge characteristics becomes significant.

In recent years, it has been increasingly required to reproduceuniformly an image including a large amount of solid portion such asbarcodes or an image such as graphic designs, instead of, for example,documents including a large amount of printed letter printed by, forexample, printers. For example, particularly in full color development,solid portions are larger than text portions, and thus the amount ofconsumed or supplied toner increases, and it is desirable that the tonermaintains the desired charge characteristics all the time under variousenvironmental conditions. In these recent electrophotographic processeswith large toner consumption and high replenishment developmentconditions, the above-described carrier having a silicone resin and asilane coupling agent such as an aminosilane coupling agent can impartsome charge to a negatively charged toner, and has some durability overa long period of use. However, the carrier cannot impart chargesufficiently to a small sized toner or a high density toner for highdefinition for use in recent printers or full color developing devicesdealing with a large amount of solid portion, and cannot increase thecharge amount instantly with respect to toner supplied at the time ofprinting. Ultimately, a sufficient durability cannot be attained atpresent.

In a carrier having a resin coated-layer in which a terminal perfluoroalkylsilane coupling agent or a fluorine-substituted alkyl group isintroduced to a silicone resin, although some improvement of theformation of spent toner can be confirmed, an appropriate charge amountcannot be obtained when used for a negatively charged toner.Furthermore, the coating film is not sufficiently uniform, and thecarrier cannot satisfactorily prevent abrasion or stripping of the resincoating layer caused by downsizing of devices to cope with the recentspace-saving trend and by increased stress on the carrier in adeveloping device in accordance with realization of high speedperformance.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a carrier forelectrophotography in which the above-described conventional problemsare solved, in which the charge amount does not decrease at hightemperature or high humidity nor extremely increase at low temperatureor low humidity, in which the charge amount can increase instantly withrespect to toner supplied at the time of printing, in which the tonerconsumption amount is excellent due to high transfer efficiency, inwhich a long lifetime of the carrier is realized based on a highdurability that prevents deterioration of a developing agent caused bystripping of a coating layer and that also prevents a deteriorationcaused by the formation of spent toner of the toner, and in which thecarrier charges a toner negatively.

In order to achieve the above-described objects, in a carrier forelectrophotography according to the present invention, a surface of atleast a core material is coated with a resin, the coating resin containsa fluorine modified silicone resin and an aminosilane coupling agent,and the carrier charges a toner negatively.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view showing an image forming apparatusthat is used in Working Example 1 of the present invention. 301:photosensitive member, 304: laser signal light, 305: development roller,306: blade, 308: carrier, 309: toner, 310: high voltage power supply

BEST MODE FOR CARRYING OUT THE PRESENT INVENTION

The inventors of the present invention have keenly examined theabove-described carrier to improve it, and found the following. In aresin-coated carrier coated with a negatively charged fluorine modifiedsilicone resin containing a positively charged aminosilane couplingagent, the charge amount can increase instantly with respect to tonersupplied at the time of printing (charge amount rising characteristics),since the difference on the triboelectric series between the toner andthe carrier is reduced, and since the distribution of the charge amountsbecomes sharp. Moreover, the resin-coated carrier has a good tonerconsumption amount and a high durability, since transfer efficiency isexcellent based on excellent toner stripping properties. Thus, thepresent invention was achieved.

In the present invention, it is preferable that the resin coating layerfurther comprises conductive microp articles within a range of 1 to 15weight parts with respect to 100 weight parts of the coating resin.

It is preferable that the aminosilane coupling agent is included in arange of 5 to 40 weight parts with respect to 100 weight parts of thecoating resin.

Furthermore, it is preferable that the proportion of the coating resinis within a range of 0.1 to 5.0 weight parts with respect to 100 weightparts of the carrier core material.

Furthermore, it is preferable that a releasing agent wax is added to thetoner within a range of 4 to 20 weight parts with respect to 100 weightparts of a binding resin of the toner.

Furthermore, it is preferable that inorganic microparticles which havebeen subjected to a hydrophobic treatment, and whose average particlesize ranges from 6 to 120 nm, are adhered on the surface of the tonerwithin a range of 0.5 to 4.5 weight parts with respect to 100 weightparts of the toner.

Hereinafter, the present invention will be described in further detail.

A carrier for electrophotography according to the present invention hasa resin coating layer on a carrier core material, the resin coatinglayer being made of a fluorine modified silicone resin containing anaminosilane coupling agent.

Examples of the carrier core material used in the present inventioninclude an iron powder carrier core material, a ferrite carrier corematerial, a magnetite carrier core material, and a compound carrier corematerial. It is preferable to use a ferrite carrier core material sinceits substantially spherical shape makes it easy to obtain appropriatemagnetization properties and electrical resistance properties, which isadvantageous in light of providing performance, charge amount risingcharacteristics, image quality, and a long lifetime.

Herein, the ferrite carrier core material generally can be expressed,for example, by the following formula:(MO)_(X)(Fe₂O₃)_(Y)

In the formula, M includes at least one selected from Cu, Zn, Fe, Mg,Mn, Ca, Li, Ti, Ni, Sn, Sr, Al, Ba, Co, Mo, and the like. X and Y referto a molar ratio by weight, and satisfy the condition that X+Y=100.

M preferably includes one or more selected from Li, Mg, Ca, Mn, Sr, andSn. It is preferable that in the ferrite particles, the content ofcomponents other than the above is 1 weight percent or less.

As a raw material, the ferrite carrier core material includes Fe₂O₃ asthe main component, to which an oxide of M is mixed with M beingselected from Cu, Zn, Fe, Mg, Mn, Ca, Li, Ti, Ni, Sn, Sr, Al, Ba, Co,Mo, for example. As an example of a method for producing the ferritecarrier core material, raw materials such as the above oxides are firstprovided in an appropriate amount, milled by using a wet ball mill for10 hours, mixed, dried, and then kept at 950° C. for 4 hours.Subsequently, the obtained material is milled by using a wet ball millfor 24 hours, and binding agents such as polyvinyl alcohol, anantifoaming agent, and a dispersing agent are added, so that a slurrywith a raw material particle size of 5 μm or less is obtained. Thisslurry is dried and granulated so as to form a granulated substance,kept at 1300° C. for 6 hours at a controlled oxygen concentration,milled, and then classified to obtain a desired particle sizedistribution.

As a resin used for a resin coating layer of the present invention, afluorine modified silicone resin is necessary. It is preferable that thefluorine modified silicone resin is a crosslinked fluorine modifiedsilicone resin obtained by reacting polyorganosiloxane and an organicsilicon compound containing a perfluoro alkyl group. It is preferablethat the polyorganosiloxane and the organic silicon compound containinga perfluoro alkyl group are mixed so that the organic silicon compoundcontaining a perfluoro alkyl group is present within a range of 3 to 20weight parts with respect to 100 weight parts of the polyorganosiloxane.

It is preferable that the polyorganosiloxane includes at least onerepeating unit selected from Chemical Formulas 1 and 2 below.

R¹ and R² denote a hydrogen atom, a halogen atom, a hydroxy group, amethoxy group, or a C1 to C4 alkyl group or phenyl group, R³ and R⁴denote a C1 to C4 alkyl group or phenyl group, and m denotes an averagepolymerization degree and is a positive integer, preferably ranging from2 to 500, and more preferably ranging from 5 to 200.

R¹ and R² denote a hydrogen atom, a halogen atom, a hydroxy group, amethoxy group, or a C1 to C4 alkyl group or phenyl group, R³, R⁴, R⁵ andR⁶ denote a C1 to C4 alkyl group or phenyl group, and n denotes anaverage polymerization degree and is a positive integer, preferablyranging from 2 to 500, and more preferably ranging from 5 to 200.

Examples of the organic silicon compound containing a perfluoro alkylgroup include CF₃CH₂CH₂Si(OCH₃)₃, C₄F₉CH₂CH₂Si(CH₃)(OCH₃)₂,C₈F₁₇CH₂CH₂Si(OCH₃)₃, C₈F₁₇CH₂CH₂Si(OC₂H₅)₃, and(CF₃)₂CF(CF₂)₈CH₂CH₂Si(OCH₃)₃. It is particularly preferable that theorganic silicon compound includes a trifluoropropyl group.

Furthermore, in this embodiment, the resin coating layer contains anaminosilane coupling agent. This aminosilane coupling agent may be aknown coupling agent such asγ-(2-aminoethyl)aminopropyltrimethoxysilane,γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, andoctadecylmethyl[3-(trimethoxysilyl)propyl] ammonium chloride (from thetop, SH6020, SZ6023, AY43-021: produced by Dow Corning Toray SiliconeCo., Ltd.), and KBM602, KBM603, KBE903, KBM573 (produced by Shin-EtsuSilicones). In particular, primary amines are preferable. The polarityof secondary or tertiary amines having substituents such as a methylgroup, an ethyl group, or a phenyl group is so poor that the effect ofthe charge amount rising characteristics of the toner is small.Furthermore, when the portion of the amino group is an aminomethylgroup, an aminoethyl group, or an aminophenyl group, then the silanecoupling agent has a primary amine at its end, but the amino groups inthe straight-chain organic groups extending from the silane do notaffect the charge amount rising characteristics of the toner, but ratherare affected by moisture at high humidity, so that even though thecarrier has the capability of imparting a charge on the toner initiallydue to the amino group at the end, this charge imparting capabilitydeteriorates at the time of printing, so that the carrier ultimatelywill have a short lifetime.

By using such aminosilane coupling agents, a negatively chargeddeveloping agent can be obtained in which the charge amount can increaseinstantly with respect to toner supplied at the time of printing (chargeamount rising characteristics) since a negative charge is imparted tothe toner while securing a sharp distribution of the charge amounts ofthe positively charged fluorine modified silicone resin layer, and sincea difference on the triboelectric series between the toner and thecarrier is reduced, and in which the toner consumption amount isexcellent due to the excellent transfer efficiency based on excellenttoner stripping properties. Furthermore, the aminosilane coupling agenthas an effect that is similar to a crosslinking agent, and thus thecrosslinking degree of the fluorine modified silicone resin layerserving as a base layer is improved, reducing abrasion or stripping by along period of use which generally tends to occur when a fluororesin isused, and the charge is stabilized, thus improving durability.

The aminosilane coupling agent is used within a range of 5 to 40 weightparts, preferably 10 to 30 weight parts, with respect to 100 weightparts of the coating resin. When its content is less than 5 weightparts, the effect of the aminosilane coupling agent cannot be exerted.When its content is more than 40 weight parts, the crosslinking degreeof the resin coating layer becomes so high that a charge-up effect tendsto occur, and thus image defects such as an insufficient development maybe caused.

Furthermore, the coating hardness of a fluorine modified silicone resinhaving relatively high insulation is improved further by adding anaminosilane coupling agent, and thus abrasion resistance, strippingresistance, and resistance against the formation of spent toner of theresin coating layer are improved, so that sufficient durability for along period of use, which is one object of the present invention, issecured. However, according to this, the resin coating layer tends to bemore insulating, and thus the development properties sometimes aredeteriorated. Accordingly, it is preferable that the resin coating layercontains conductive microparticles. Examples of such conductivemicroparticles include carbon blacks such as oil furnace carbon andacetylene black, semiconductive oxides such as titanium oxide and zincoxide, and materials in which a surface of powders such as titaniumoxide, zinc oxide, barium sulphate, aluminum borate, and potassiumtitanate are coated with stannic oxide, carbon black, or a metal. It ispreferable that the specific resistance thereof is 10¹⁰ Ωcm or less.When the conductive microparticles are used, it is preferable that theircontent ranges from 1 to 15 weight parts with respect to 100 weightparts of the coating resin. When the content of the conductivemicroparticles with respect to the resin coating layer is within acertain range, the hardness of the resin coating layer is improved bythe filler effect. However, when their content is greater than 15 weightparts, a formation of the resin coating layer is impeded, and thus theadhesiveness or the hardness may be deteriorated. Furthermore, when theconductive microparticles are contained excessively in a full colordeveloping agent, they may cause color stains of the toner to betransferred and adhered on a paper surface. When their content is lessthan 1 weight part, the effect of reducing the high insulation of theresin coating layer is small, and thus deterioration of the developmentproperties cannot be prevented.

It is preferable that an average particle size of the carrier used inthe present invention is 20 to 70 μm. When the average particle size ofthe carrier is smaller than 20 μm, the ratio of microparticles in thecarrier particle distribution becomes high, and thus these carrierparticles have low magnetization per particle, so that the carrier tendsto be developed too easily on the photosensitive member. Furthermore,when the average particle size of the carrier is more than 70 μm, thespecific surface area of the carrier particles becomes small, and thustheir toner holding power is reduced, so that toner scattering iscaused. Also, in full color development including a large amount ofsolid image, the solid image is reproduced in a particularly poormanner, which is not preferable. “Solid image” refers to the image inwhich the toner is printed on a relatively large area. Morespecifically, it refers to a toner image that has a larger area than aline image such as a letter.

There is no particular limitation regarding the method for forming thecoating layer on the carrier core material, and it may include knowncoating methods of wet coating methods and dry coating methods. Examplesof wet coating methods include an immersion method in which a powderedcarrier core material is immersed in a solution for forming a coatinglayer, a spray method in which a solution for forming a coating layer issprayed onto a surface of a carrier core material, a fluid bed method inwhich a solution for forming a coating layer is sprayed onto a carriercore material being floated by using fluid air, and a kneader coatermethod in which a carrier core material and a solution for forming acoating layer are mixed in a kneader coater and then the solvent isremoved. In a dry coating method, for example, a powdered resin and acarrier core material are mixed at a high speed, and by using frictionalheat generated by this, the powdered resin is fused and coats thesurface of the carrier core material. Although any or these methods canbe applied, it is particularly preferable to use a wet coating method,when coating a fluorine modified silicone resin containing anaminosilane coupling agent in the present invention.

There is no particular limitation regarding the solvent that is used asa coating liquid for forming a coating layer as long as it dissolves thecoating resin, and it may be selected in accordance with a coating resinthat is used. Examples of the solvent typically include aromatichydrocarbons such as toluene and xylene, ketones such as acetone andmethyl ethyl ketone, and ethers such as tetrahydrofuran and dioxane.

It is preferable that the content of the coating resin of the presentinvention ranges from 0.1 to 5.0 weight parts with respect to 100 weightparts of the carrier core material. When the coating resin is less than0.1 weight parts, it is difficult to form a uniform coating layer on thesurface of the carrier, and thus the influence of the characteristics ofthe carrier core material becomes so dominant that the fluorine modifiedsilicone resin and the aminosilane coupling agent of the presentinvention may not be sufficiently effective. When its content is morethan 5.0 weight parts, the coating layer becomes so thick that thecarrier particles granulate with each other, and thus uniform carrierparticles may not be obtained.

After coating the surface of the carrier core material with the fluorinemodified silicone resin containing the aminosilane coupling agent inthis manner, it is preferable to perform a baking process. There is noparticular limitation regarding the means for performing the bakingprocess, and it may be either an internal heating process or an externalheating process. For example, it is possible to perform the bakingprocess by using an electric furnace with a fixed or a fluidized bed, arotary kiln electric furnace, a burner furnace, or a microwave furnace.However, regarding the temperature for the baking process, in order toachieve the fluorosilicone's effect of improving resistance against theformation of spent toner of the resin coating layer efficiently, theprocess is performed at a high temperature preferably ranging from 200to 350° C., more preferably ranging from 220 to 280° C.

A wax serving as a releasing agent is added to the toner of thisembodiment. Examples of the wax preferably include a polyolefin wax suchas polyethylene or polypropylene wax, a synthetic hydrocarbon wax suchas a paraffin wax, a montan wax or a Fischer-Tropsch wax, and higherfatty acids and their metal compounds, such as stearic acid, palmiticacid, lauric acid, aluminum stearate, barium stearate, zinc stearate, orzinc palmitate. It is preferable to use a wax whose melting point rangesfrom 60 to 120° C. measured by DSC measurement (with a differentialscanning calorimeter). If the melting point is lower than 60° C., hightemperature storage properties of the toner are deteriorated, and if themelting point is higher than 120° C., the effect of the fixation offsetproperty is deteriorated. It is preferable that the added amount iswithin a range of 4 to 20 weight parts with respect to 100 weight partsof the binding resin of the toner. When the added amount is less thanthe above range, the effect of the fixation offset property isdeteriorated. When the added amount is more than the above range, thehigh temperature storage properties of the toner are deteriorated, andthus fog increases when developing and the transfer efficiency isdeteriorated.

Furthermore, as machines perform at higher speeds and are adapted forcolor printing, it is required that the toner secures a broad margin fora fixation offset and that the developing agent has a longer lifetime.Therefore, it is necessary to add a large amount of wax having a lowmelting point to the toner. When toner containing a wax having a lowmelting point is used in combination with a conventional carrier,stirring stress in a developing device causes formation of spent toneron the surface of the carrier within a short period of use, and thus adeterioration of the developing agent is caused. However, by using incombination with the carrier of this embodiment, the formation of spenttoner can be prevented, and at the same time, a broad margin for thefixation offset can be secured.

The binding resin of this embodiment contains a polyester resin in whichat least one molecular weight maximum peak is in a region of 2×10³ to3×10⁴ in a molecular weight distribution measured with GPC, in which thecontent of components in the high molecular weight region with amolecular weight of at least 3×10⁴ is at least 5% with respect to theentire binding agent, in which the weight-average molecular weightranges from 10,000 to 500,000, in which the Z-average molecular weightranges from 20,000 to 5,000,000, in which the ratio between theweight-average molecular weight and the number-average molecular weight(weight-average molecular weight/number-average molecular weight) rangesfrom 3 to 150, in which the ratio between the Z-average molecular weightand the number-average molecular weight (Z-average molecularweight/number-average molecular weight) ranges from 10 to 2000, in whichthe melting temperature (hereinafter, referred to as the softeningpoint) ranges from 80 to 150° C. measured by the 1/2 method with acapillary rheometer flow-tester of a constant pushing force type, inwhich the flow-beginning temperature ranges from 80 to 120° C., and inwhich the glass transition point of the resin ranges from 45 to 68° C.The resin preferably contains a polyester resin in which theweight-average molecular weight ranges from 10,000 to 150,000, in whichthe Z-average molecular weight ranges from 20,000 to 4,000,000, in whichthe ratio of (weight-average molecular weight)/(number-average molecularweight) ranges from 3 to 50, in which the ratio of (Z-average molecularweight)/(number-average molecular weight) ranges from 10 to 1500, inwhich the softening point ranges from 90 to 140° C., in which theflow-beginning temperature ranges from 85 to 115° C., and in which theglass transition point ranges from 52 to 65° C. The resin morepreferably contains a polyester resin in which the weight-averagemolecular weight ranges from 10,000 to 120,000, in which the Z-averagemolecular weight ranges from 100,000 to 3,200,000, in which the ratio of(weight-average molecular weight)/(number-average molecular weight)ranges from 3 to 20, in which the ratio of (Z-average molecularweight)/(number-average molecular weight) ranges from 10 to 1000, inwhich the softening point ranges from 105 to 135° C., in which theflow-beginning temperature ranges from 90 to 120° C., and in which theglass transition point ranges from 58 to 65° C.

When using a binding resin in which the weight-average molecular weightis smaller than 10,000, in which the Z-average molecular weight issmaller than 20,000, in which the ratio of (weight-average molecularweight)/(number-average molecular weight) is smaller than 3, in whichthe ratio of (Z-average molecular weight)/(number-average molecularweight) is smaller than 10, in which the softening point is lower than80° C., in which the flow-beginning temperature is lower than 80° C., orin which the glass transition point is lower than 45° C., then thedispersibility of the wax or the electric charge controlling agent inthe resin is deteriorated, and thus fog or toner scattering increases,offset resistance or high temperature storage properties aredeteriorated, and filming on a photosensitive member occurs.

When using a binding resin in which the weight-average molecular weightis larger than 500,000, in which the Z-average molecular weight islarger than 5,000,000, in which the ratio of (weight-average molecularweight)/(number-average molecular weight) is larger than 150, in whichthe ratio of (Z-average molecular weight)/(number-average molecularweight) is larger than 2000, in which the softening point is higher than150° C., in which the flow-beginning temperature is higher than 120° C.,or in which the glass transition point is higher than 68° C., then anexcessive load may be applied during processing in the device, and thusthe productivity decreases extremely or the adhesive strength decreases.

The binding resin that preferably is used in this embodiment is apolyester resin obtained by a condensation polymerization between analcohol component and a carboxylic acid component such as carboxylicacid, carbonate, or carboxylic anhydride.

Examples of dibasic carboxylic acids or lower alkyl esters includealiphatic dibasic acids such as malonic acid, succinic acid, glutaricacid, adipic acid, and hexahydrophthalic anhydride, aliphaticunsaturated dibasic acids such as maleic acid, maleic anhydride, fumaricacid, itaconic acid, and citraconic acid, aromatic dibasic acids such asphthalic anhydride, phthalic acid, terephthalic acid, and isophthalicacid, and their methyl ester and ethyl ester. Of these, it is preferableto use aromatic dibasic acid or their lower alkyl ester such as succinicacid, phthalic acid, terephthalic acid, or isophthalic acid. It ispreferable to use succinic acid and terephthalic acid together, or touse phthalic acid and terephthalic acid together.

Examples of tribasic or higher carboxylic acid components include1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid,1,2,4-cyclohexanetricarboxylic acid, 2,5,7-naphthalenetricarboxylicacid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylicacid, 1,2,5-hexatricarboxylic acid,1,3-dicarboxylic-2-methyl-2-methylene carboxpropane, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid,Enpol trimer acid and their acid anhydrides and alkyl (C1 to C12)esters.

Examples of the dihydric alcohol include diols such as ethylene glycol,1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol,1,4-butylene glycol, 1,6-hexanediol, neopentyl glycol, diethyleneglycol, dipropylene glycol, bisphenol A ethylene oxide additive, andbisphenol A propylene oxide additive, triols such as glycerin, andtrimethylolpropane, trimethylolethane, and mixtures of these. Of these,it is particularly preferable to use a bisphenol A as shown in ChemicalFormula 3, its derivatives, its alkylene oxide additives, neopentylglycol, or trimethylolpropane.

R denotes an ethylene group or a propylene group, and x and yrespectively denote an integer that is 1 or larger, and the averagevalue of x+y ranges from 2 to 10.

Examples of a trihydric or higher alcohol component include sorbitol,1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol,tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol,2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane,trimethylolpropane, 1,3,5-trihydroxymethyl benzene.

The polymerization may be performed by a known process, such ascondensation polymerization or solution condensation polymerization.Thus, a superior toner can be obtained without damaging PVC matresistance or the color of a coloring material of a color toner.

Polybasic carboxylic acid and polyhydric alcohol typically are used insuch a proportion that the ratio of hydroxyl groups to carboxyl groups(OH/COOH) by number ranges from 0.8 to 1.4.

The molecular weights of the resin, wax, and toner are values obtainedby measurements using gel permeation chromatography (GPC) using aplurality of kinds of monodisperse polystyrene as the standard sample.

The measurement is performed by using an apparatus of the HPLC8120series (produced by Tosoh Corporation); with columns of TSKgel superHM-HH4000/H3000/H2000 (diameter: 7.8 mm, 150 mm×3); with an eluent of THF(tetrahydrofuran) at a flow-rate of 0.6 ml/min, a sample concentrationof 0.1%, and an added amount of 20 μL; with a detector of RI; and at ameasuring temperature of 40° C. As a pretreatment, a sample is dissolvedin THF and filtered through a filter of 0.45 μm to remove additives suchas silica from the sample. Subsequently, the obtained resin component ismeasured. The measurement is performed under the condition that themolecular weight distribution of the sample to be measured is includedwithin a range in which a straight line is formed by the count numberand the logarithm of the molecular weight in the measuring curveobtained by a plurality of monodisperse polystyrene standard samples.

Furthermore, the softening point of the binding resin is measured asfollows by using a flow-tester (produced by Shimadzu corporation:CFT500). While heating 1 cm³ of a sample at a temperature-increase rateof 6° C./min, a load of approximately 9.8×10⁵ N/m² is applied by aplunger to extrude the sample from a die having a diameter of 1 mm and alength of 1 mm. Based on the relationship between the piston stroke ofthis plunger and the temperature rising properties, a flow-beginningtemperature (Tfb) is a temperature when the piston stroke starts torise. According to the ½ method, the melting temperature (softeningpoint Tm) is the temperature at a point obtained by adding the lowestvalue in the curve to the ½ value of a difference between the lowestvalue of the curve and the flow ending point.

The glass transition point of the resin is measured by using adifferential scanning calorimeter. A sample is heated to 100° C. and iskept at the same temperature for 3 minutes. Subsequently, the sample iscooled to room temperature at a temperature-falling rate of 10 K/min,and then is heated at a temperature-increase rate of 10 K/min. Based ona heat history measured at that time, “glass transition point” refers tothe temperature at a point of intersection between an extension line ofa base line below the glass transition point and a tangent line havingthe maximum inclination in a range of a peak rising portion to the peaktop.

According to the DSC measurement, the melting point in an endothermicpeak is measured by using a differential scanning calorimeter DSC-50(produced by Shimadzu Corporation). A sample is heated to 200° C. at atemperature-increase rate of 5 K/min and is kept at the same temperaturefor 5 minutes. Subsequently, the sample is quickly cooled to 10° C. andis left for 15 minutes. Then the sample is heated at atemperature-increase rate of 5 K/min. Based on an endothermic (melting)peak measured at that time, the melting point is obtained. The amount ofthe sample placed into a cell is 10 mg±2 mg.

Preferable examples of the binding resin used in this embodiment alsomay include a monopolymer and a copolymer of various kinds of vinylmonomers. For example, styrene and its derivatives such as styrene,o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene,2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene,p-n-hexylstyrene, p-n-octylstyrene, and p-n-hexylstyrene,p-chlorostyrene may be used, and it is particularly preferable to usestyrene.

Examples of acrylic monomer include acrylic acid, methacrylic acid,methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate,cyclohexyl acrylate, phenyl acrylate, methyl methacrylic acid, hexylmethacrylic acid, 2-ethylhexyl methacrylic acid, β-hydroxyethylacrylate, γ-hydroxypropyl acrylate, a-hydroxybutyl acrylate,β-hydroxyethyl methacrylic acid, γ-aminopropyl acrylate,γ-N,N-diethylaminopropyl acrylate, ethylene glycol dimethacrylic acidester, and tetraethylene glycol dimethacrylic acid ester. In light ofthe objects of the present invention, a styrene-acrylic copolymer ispreferably a copolymer of styrene and butyl acrylate, more preferably acopolymer that contains 75 to 85 weight percent of styrene and 15 to 25weight percent of butyl acrylate.

At that time, it is preferable that the weight-average molecular weightranges from 30,000 to 400,000, that the Z-average molecular weightranges from 50,000 to 5,000,000, that the ratio of (weight-averagemolecular weight)/(number-average molecular weight) ranges from 10 to100, that the ratio of (Z-average molecular weight)/(number-averagemolecular weight) ranges from 40 to 2000, that the softening pointranges from 90 to 140° C., and that the flow-beginning temperatureranges from 85 to 115° C., and that the glass transition point rangesfrom 52 to 65° C. It is more preferable that the weight-averagemolecular weight ranges from 30,000 to 280,000, that the Z-averagemolecular weight ranges from 50,000 to 3,000,000, that the ratio of(weight-average molecular weight)/(number-average molecular weight)ranges from 10 to 50, that the ratio of (Z-average molecularweight)/(number-average molecular weight) ranges from 40 to 500, thatthe softening point ranges from 105 to 135° C., and that theflow-beginning temperature ranges from 90 to 120° C., and that the glasstransition point ranges from 58 to 65° C.

When using a binding resin in which the weight-average molecular weightis smaller than 30,000, in which the Z-average molecular weight issmaller than 50,000, in which the ratio of (weight-average molecularweight)/(number-average molecular weight) is smaller than 10, in whichthe ratio of (Z-average molecular weight)/(number-average molecularweight) is smaller than 40, in which the softening point is lower than90° C., in which the flow-beginning temperature is lower than 85° C., orin which the glass transition point is lower than 52° C., then thedispersibility of the wax or the electric charge controlling agent inthe resin is deteriorated, and thus fog or toner scattering increases,offset resistance or high temperature storage properties aredeteriorated, and filming on a photosensitive member occurs.

When using a binding resin in which the weight-average molecular weightis larger than 400,000, in which the Z-average molecular weight islarger than 5,000,000, in which the ratio of (weight-average molecularweight)/(number-average molecular weight) is larger than 100, in whichthe ratio of (Z-average molecular weight)/(number-average molecularweight) is larger than 2000, in which the softening point is higher than140° C., in which the flow-beginning temperature is higher than 120° C.,or in which the glass transition point is higher than 65° C., then anexcessive load may be applied during processing in the device, and thusthe productivity decreases extremely or the adhesive strength decreases.

As the method for producing the polymer, it is possible to use any knownpolymerization method, such as bulk polymerization, blockpolymerization, liquid polymerization, suspension polymerization, oremulsion polymerization. It is also preferable to use a method, forexample, in which polymerization is performed up to a conversion rangingfrom 30 to 90 weight parts using bulk polymerization, and then to add asolvent and a polymerization initiator, and to continue the reactionusing liquid polymerization.

Examples of a pigment used in this embodiment include carbon black, ironblack, graphite, nigrosine, a metal complex of azo dye, acetoaceticarylamido mono azo yellow pigment such as C.I. pigment yellow 1, 3, 74,97, or 98, acetoacetic arylamido dis-azo yellow pigment such as C.I.pigment yellow 12, 13, 14, or 17, C.I. solvent yellow 19, 77, or 79, andC.I. disperse yellow 164. It is particularly preferable to usebenzimidazolone such as C.I. pigment yellow 93, 180, or 185, in light ofan effect regarding filming on a photosensitive member.

One or more kinds selected from red pigments such as C.I. pigment red48, 49:1, 53:1, 57, 57:1, 81, 122, or 5, red dyes such as C.I. solventred 49, 52, 58, or 8, and blue dye or pigment of phthalocyanine or itsderivatives such as C.I. pigment blue 15:3 is/are added. The addedamount is preferably within a range of 3 to 8 weight parts with respectto 100 weight parts of the binding resin.

Examples of an external additive of this embodiment include metal-oxidefine powders such as silica, alumina, titanium oxide, zirconia,magnesia, ferrite, or magnetite, titanates such as barium titanate,calcium titanate, or strontium titanate, zirconates such as bariumzirconate, calcium zirconate, or strontium zirconate, and mixtures ofthese. If necessary, a hydrophobic treatment is performed on theexternal additive.

Examples of a silane coupling agent for the hydrophobic treatmentinclude dimethyldichlorosilane, trimethylchlorosilane,allyldimethylchlorosilane, hexamethyldisilazane, allyl phenyldichlorosilane, benzyl methylchlorosilane, vinyl triethoxy-silane,y-methacrylic oxypropyltrimethoxysilane, vinyltriacetoxy silane,divinylchlorosilane and dimethyl vinylchlorosilane. Examples of thetreatment with the silane coupling agent include a dry treatment inwhich an evaporated silane coupling agent is reacted with microparticlesput into a cloud state by, for example, stirring, and a wet treatment inwhich a dropping reaction is performed with a silane coupling agentcontaining microparticles dispersed in its solvent.

Furthermore, it is also preferable to perform a treatment with asilicone oil material after the treatment with the silane couplingagent.

In order further to enhance the effect of the hydrophobic treatment, itis preferable to perform an additional treatment withhexamethyldisilazane, dimethyldichlorosilane, or other silicone oil. Itis preferable to perform the treatment with at least one of dimethylsilicone oil, methylphenyl silicone oil, and alkyloyl modified siliconeoil.

It is preferable that inorganic microparticles having an averageparticle size of 6 nm to 120 nm are added within a range of 0.5 to 4.5weight parts with respect to 100 weight parts of the toner hostparticles. When the average particle size is smaller than 6 nm, floatingof silica or filming on a photosensitive member tends to occur, and backtransfer while transferring cannot be completely suppressed. When theaverage particle size is larger than 120 nm, the fluidity of the toneris deteriorated. When the added amount is smaller than 0.5 weight parts,the fluidity of the toner is deteriorated, and an occurrence of transferdefects while transferring cannot be suppressed completely. When theadded amount is larger than 4.5 weight parts, floating of silica orfilming on a photosensitive member tends to occur.

Hereinafter, the present invention will be described in further detailwith reference to working examples. However, the present invention isnot limited to these.

WORKING EXAMPLES Carrier Production Example 1

First, 39.7 mol percent of MnO, 9.9 mol percent of MgO, 49.6 mol percentof Fe₂O₃, and 0.8 mol percent of SrO were milled for 10 hours using awet ball mill, mixed, dried, and pre-baked by keeping at 950° C. for 4hours. Subsequently, the obtained material was milled using the wet ballmill for 24 hours, granulated using a spray dryer, dried, and baked bykeeping in an electric furnace in an atmosphere of 2% oxygenconcentration at 1270° C. for 6 hours. Then, the material was crackedand further classified, so as to obtain a core material made of ferriteparticles whose average particle size was 50 μm, and in which thesaturation magnetization was 65 emu/g when a magnetic field of 3000oersted was applied.

Next, 250 g of polyorganosiloxane including 15.4.mol percents of(CH₃)₂SiO units shown in Chemical Formula 4 below and 84.6 mol percentsof CH₃SiO_(3/2) units shown in Chemical Formula 5 below were reactedwith 21 g of CF₃CH₂CH₂Si(OCH₃)₃, and a fluorine modified silicone resinwas obtained. This is a demethoxylation reaction in which an organicsilicon compound molecule containing a perfluoro alkyl group isintroduced to the polyorganosiloxane. Furthermore, 100 g of thisfluorine modified silicone resin on the solid basis and 10 g of anaminosilane coupling agent (γ-aminopropyltriethoxysilane) were weighed,and were dissolved in 300 cc of toluene solvent.

R¹, R², R³, and R⁴ denote a methyl group, and m denotes an averagepolymerization degree and is 100.

R¹, R², R³, R⁴, R⁵, and R⁶ denote a methyl group, and n denotes anaverage polymerization degree and is 80.

Subsequently, 10 kg of the above-described ferrite particles were coatedby stirring them in the above-described coating resin solution for 20minutes using immersion dry coating equipment. Subsequently, theobtained material was baked at 260° C. for 1 hour, and carrier 1 wasobtained.

Carrier Production Example 2

A core material was produced and coated by the same processes as inCarrier Production Example 1 except that the CF₃CH₂CH₂Si(OCH₃)₃ waschanged to C₈F₁₇CH₂CH₂Si(OCH₃)₃, and carrier 2 was obtained.

Carrier Production Example 3

A core material was produced and coated by the same processes as inCarrier Production Example 1 except that conductive carbon (produced byKetjenblack International Company: EC) was dispersed at a ratio of 5%with respect to the solid compound of the resin by using a pearl mill,and carrier 3 was obtained.

Carrier Production Example 4

A core material was produced and coated by the same processes as inCarrier Production Example 3 except that the amount of the addedaminosilane coupling agent was changed to 5 g, and carrier 4 wasobtained.

Carrier Production Example 5

A core material was produced and coated by the same processes as inCarrier Production Example 3 except that the amount of the addedaminosilane coupling agent was changed to 30 g, and carrier 5 wasobtained.

Carrier Production Example 6

A core material was produced and coated by the same processes as inCarrier Production Example 3 except that the amount of the addedaminosilane coupling agent was changed to 50 g, and carrier 6 wasobtained.

Carrier Production Example 7

A core material was produced and coated by the same processes as inCarrier Production Example 1 except that the coating resin was changedto a straight silicone resin (produced by Dow Corning Toray SiliconeCo.,Ltd.: SR-2411), and carrier 7 was obtained.

Carrier Production Example 8

A core material was produced and coated by the same processes as inCarrier Production Example 7 except that conductive carbon (produced byKetjenblack International Company: EC) was dispersed at a ratio of 5%with respect to the solid compound of the resin by using a pearl mill,and carrier 8 was obtained.

Carrier Production Example 9

A core material was produced and coated by the same processes as inCarrier Production Example 1 except that the coating resin was changedto a copolymer of perfluoro octylethylethyl acrylate and methacrylate,and carrier 9 was obtained.

Carrier Production Example 10

A core material was produced and coated by the same processes as inCarrier Production Example 1 except that the coating resin was changedto an acrylic modified silicone resin (produced by Shin-Etsu ChemicalCo., Ltd.: KR-9706), and carrier 10 was obtained.

Working Example 1

A toner is produced through a preliminary mixing process, a melting andkneading process, a milling and classifying process, and an externaladding process. In the preliminary mixing process, a binding resin andan additive to be dispersed into this resin are dispersed in a uniformmanner by using, for example, a mixer provided with a stirring blade.Examples of such a mixer include known mixers such as a Super Mixer(produced by Kawata Manufacturing Co., Ltd.), a Henschel Mixer (producedby Mitsui Mining Co., Ltd.), a PS mixer (produced by Shinko Pantec Co.,Ltd.), and a Lodige Mixer.

In the kneading process, a twin-screw extruding kneader (produced byIkegai Co., Ltd.: PCM45) is preferably used. The kneaded material isroughly milled by using, for example, a cutter mill, and is finelymilled by using, for example, a jet mill (produced by Nippon PneumaticMfg. Co., Ltd.: IDS mill, for example). Subsequently, the obtainedmicroparticles are omitted by using a pneumatic classifier, ifnecessary, and toner particles (toner host particles) with desiredparticle size distribution are obtained. In the classifying process,toner particles (toner host particles) with a volume average particlesize of 8 μm were obtained.

In the external adding process, the toner particles (the toner hostparticles) obtained through the classification process are mixed with anexternal additive such as silica. A known mixer such as a Henschel Mixeror a Super Mixer is used for this process.

Table 1 below shows characteristics of the binding resin used in thisworking example. Resins JE-1 and JE-2 were a polyester resin containingbisphenol A propylene oxide additive, terephthalic acid, trimelliticacid, succinic acid, and fumaric acid as the main components, whosethermal characteristics and mix proportion were varied by thepolymerization conditions. Resins JS-1, JS-2, and JS-3 are copolymers ofstyrene and butylacryl acid, whose thermal characteristics and mixproportion were varied. TABLE 1 resin JE-1 JE-2 JS-1 JS-2 JS-3 Mn (×10⁴)0.32 0.31 0.59 0.52 0.32 Mw (×10⁴) 6.40 10.20 18.50 25.50 4.20 Mz (×10⁴)97.50 302.50 189.20 250.50 82.10 Wm = Mw/Mn 20.00 31.88 31.36 48.6513.13 Wz = Mz/Mn 304.69 945.31 320.68 481.73 256.56 Tg (° C.) 58.0063.00 59.80 62.80 58.00 Tm (° C.) 119.80 121.50 130.50 135.40 107.00 Tfb(° C.) 100.00 105.40 112.50 110.50 890.00 AV (mg KOH/g) 15 20 3 6 1

Mn denotes number-average molecular weight, Mw denotes weight-averagemolecular weight, Mz denotes Z-average molecular weight, Wm denotes theratio between the weight-average molecular weight Mw and thenumber-average molecular weight Wn (Mw/Mn), Wz denotes the ratio betweenthe Z-average molecular weight Mz and the number-average molecularweight Mn of the binding resin (Mz/Mn), and AV denotes a resin acidvalue. Table 2 below lists the waxes used in this working example. TABLE2 wax material product name (manufacturer name) WA-1 polypropylene waxVISCOL 550P (Sanyo Chemical Industries, Ltd.) WA-2 polypropylene wax LEL400P (Sanyo Chemical Industries, Ltd.)

As a pigment in this working example, Carbon Black #40 (produced byMitsubishi Chemical Co., Ltd.) was used at a ratio of 5 weight partswith respect to 100 weight parts of the binding resin.

The external additive used in this working example was R974 (16 nm,treated with dimethyldichlorosilane) and RX50 (40 nm, treated withhexamethyldisilazane) both of which were produced by Nippon Aerosil Co.,Ltd. Their contents were 1.0 weight parts each with respect to 100weight parts of the toner host particles. The external adding process 15was performed by using a stirring blade ZOSO-type of FM20B, at arevolving speed of 2000 min⁻¹, at a processing time of 5 minutes, and ata loading amount of 1 kg.

Table 3 below shows toner material compositions and carriers used inthis working example. TABLE 3 developing toner resin wax carrier agentT1 JE1 WA1 (5) carrier 1 D1 T2 JE2 WA2 (15) carrier 2 D2 T3 JE1 WA1 (7)carrier 3 D3 T4 JE2 WA2 (6) carrier 4 D4 T5 JS1 WA1 (18) carrier 5 D5 T6JS2 WA2 (15) carrier 1 D6 T1 JE1 WA1 (5) carrier 6 d7 T7 JS3 WA2 (12)carrier 7 d8 T2 JE2 WA2 (15) carrier 8 d9 T8 JS1 WA1 (15) carrier 9 d10T3 JE1 WA1 (7) carrier 10 d11

As a mix proportion by weight of the waxes, a ratio of an added amount(weight parts) with respect to 100 weight parts of the binding resin isshown in parenthesis.

FIG. 1 is a cross-sectional view showing the structure of anelectrophotographic apparatus used in this working example. Theapparatus in this working example is a modified FPD605 copier (producedby Matsushita Electric Industrial Co., Ltd.). The mixing proportionbetween toner and carrier was 92:8.

An organic photosensitive member 301 has an aluminum conductivesupporting material, on which a charge-generating layer is formed byvapor-depositing oxotitanium phthalocyanine powder, on which acharge-transporting layer including a mixture of a polycarbonate resin(produced by Mitsubishi Gas Chemical Company, Inc.: Z-200), butadiene,and hydrazone is further layered in this order. Numeral 302 denotes acorona charger for charging the photosensitive member negatively,numeral 303 denotes a grid electrode for controlling charge potential ofthe photosensitive member, and numeral 304 denotes a signal light.Numeral 305 denotes a development sleeve, numeral 306 denotes a magneticdoctor blade, numeral 307 denotes a magnet roller for holding a carrier,numeral 308 denotes a carrier, numeral 309 denotes a toner, numeral 310denotes a voltage generator, numeral 311 denotes a waste toner leftafter transfer, and numeral 312 denotes a cleaning rubber elastic blade.It is preferable that a gap between the development sleeve and themagnetic doctor blade ranges from 0.3 to 0.5 mm, and that a gap betweenthe development sleeve and the photosensitive member ranges from 0.2 to0.5 mm. In this working example, the former was set to 0.3 mm and thelatter was set to 0.4 mm. The amount of the developing agent that wasused is 600 g.

Numeral 313 denotes a transfer roller for transferring a toner image onthe photosensitive member to paper, in which a surface of the roller isbrought into contact with a surface of the photosensitive member 301.The transfer roller 313 is an elastic roller in which a conductiveelastic member is provided around a shaft made of a conductive metal. Apressing force applied to the photosensitive member 301 by the onetransfer roller 313 (approximately 216 mm) ranges from 0 to 2000 g, andpreferably ranges from 500 to 1000 g. The force was measured from avalue obtained by multiplying a spring coefficient by a shrinking amountof a spring for applying a force so that the transfer roller 313 isbrought into contact with the photosensitive member 301. A contact widthwith the photosensitive member 301 ranges from approximately 0.5 mm to 5mm. The rubber hardness of the transfer roller 313 measured according toAsker C (a measurement by using a block piece instead of a roller form)is 80 degrees or less, and preferably ranges from 30 to 40 degrees. Theelastic roller 213 was formed of urethane elastomer in which lithiumsalt such as Li₂O salt was internally added around the shaft having adiameter of 6 mm, so that its resistance value was 10⁶ to 10⁸ Ω (theshaft and the surface were provided with an electrode to which a voltageof 500 V was applied). The outer diameter of the entire transfer roller313 was 16.4 mm, and the hardness measured according to Asker C was 40degrees. The transfer roller 313 was brought into contact with thephotosensitive member 301 by pressing the shaft of the transfer roller313 with the metal spring. The pressing force was approximately 1000 g.Examples of the elastic body for the roller include not only theabove-described foamed urethane elastomer but also an elastic body madeof another material such as CR rubber, NBR, Si-rubber, or fluororubber.Examples of the conductivity imparting agent for imparting conductivityinclude not only the above-described lithium salt but also anotherconductive material such as carbon black. Numeral 314 denotes an entryguide made of a conductive member for sending transfer paper to thetransfer roller 313, and numeral 315 denotes a conveying guide in whicha surface of a conductive member is coated for insulation. The entryguide 314 and the conveying guide 315 are grounded directly or via aresistor. Numeral 316 denotes transfer paper, and numeral 317 denotes avoltage generating power source for applying a voltage to the transferroller 313.

The photosensitive member 301 having a diameter of 60 mm, was rotated inthe direction indicated by the arrow in FIG. 1 at a circumferentialspeed of 360 mm/s. The photosensitive member 301 was charged to −700 Vby using the corona charger 303 (applied voltage: −4.5 kV, voltage ofgrid 4:−700 V). This photosensitive member 301 was irradiated with thesignal light 304 to form an electrostatic latent image. At that time, anexposure potential of the photosensitive member 301 was −100 V. Thetoner 309 was developed on the surface of this photosensitive member301.

An image was developed by using the above-described image formingapparatus. Table 4 below shows a result of a durability test. TABLE 4charge amount carrier on toner (μC/g) Spent stripping resistance after 1transfer carrier developing amount amount change initial millionefficiency toner No. agent (%) (%) rate (%) stage sheets (%) T1 1 D1 1.71.3 1.6 −32.9 −30.2 92.5 T2 2 D2 1.5 1.0 1.8 −30.8 −26.8 91.5 T3 3 D31.2 1.2 1.7 −25.8 −21.9 90.2 T4 4 D4 1.5 2.3 2.1 −28.5 −24.9 90.8 T5 5D5 1.5 0.9 1.4 −35.2 −32.8 92.0 T6 1 D6 1.6 1.5 1.6 −39.8 −36.4 92.8 T16 d7 2.0 1.1 1.5 −45.5 −52.8 61.7 T7 7 d8 4.5 5.2 18.0 −24.6 −11.8 62.5T2 8 d9 4.2 5.2 20.5 −18.5 −10.2 59.5 T8 9 d10 3.8 6.7 16.0 −25.8 −10.563.5 T3 10 d11 5.0 5.8 32.4 −19.4 −9.8 61.5

The charge amount was measured by a blow-off method for triboelectriccharging with a ferrite carrier. For the durability test, 0.3 g ofsamples were collected at a temperature of 25° C. and a relativehumidity of 45% RH, and were blown with nitrogen gas at 1.96×10⁴ (Pa)for 1 minute.

The spent amount (the spent effect of the toner) and the strippingamount (stripping of a resin coating layer) were calculated as follows.

First, a reflected electron image was picked up by using an electronmicroscope (produced by JEOL Ltd.: JSM-6 100) at an applied voltage of 5kV. This image was read by a scanner, and was transformed into an imageonly of carrier particles by using image analysis software (produced byMedia Cybernetics: Image-Pro Plus). Subsequently, a ternary codingprocess was performed to divide the image into a white portion (aportion of core material exposed), a black portion (a spent portion),and a gray portion (a coating resin portion), and then the respectiveareas were calculated. By using these values, a spent area ratio (ratioof toner spent occupying the surface of the carrier) and a coating resinarea ratio (ratio of the coating resin occupying the surface of thecarrier) were calculated based on the following formulas.Spent area ratio (%)={black portion area/(white portion area+blackportion area+gray portion area)}Coating resin area ratio (%)={gray portion area/(white portionarea+black portion area+gray portion area)}

By using the above formulas, the area ratios of carriers of the initialstage and after the durability test were calculated, and the spentamount and the stripping amount were obtained as differences in the arearatio between the carrier at the initial stage and the carrier after thedurability test.Spent amount (%)=(spent area ratio of carrier after durabilitytest)−(spent area ratio of carrier at initial stage)Stripping amount (%)=(coating resin area ratio of carrier afterdurability test)−(coating resin area ratio of carrier at initial stage)

It is preferable that the spent amount is 2.0% or less, and that thestripping ratio is 3.0% or less.

The rate of the carrier resistance change was calculated as follows.

The carrier resistance was measured in a state in which 200 mg of acarrier as a sample was inserted into a gap between electrodes of 2.0mm, in which a magnetic field having a surface flux density of 1600gauss was activated, in which carriers were connected in a linearmanner, and in which a dc voltage of 500 V was applied. Next, by usingthe above-described method, the resistance of the carrier at the initialstage and the carrier after the durability test was measured, and therate of carrier resistance change was calculated based on the followingformula:Rate of carrier resistance change(%)=(carrier resistance of carrierafter durability test)/(carrier resistance of carrier at initial stage)

It is preferable that the rate of carrier resistance change ranges from0.1 to 10%.

When an image was developed by using the developing agents D1 to D5, theobtained image achieved extremely high definition and high image qualityin which, for example, a disturbance in horizontal line, tonerscattering, or letter missing was not caused, in which a solid blackimage was reproduced uniformly, and in which even 16 lines/mm werereproduced. Furthermore, the obtained image achieved a high imagedensity of 1.3 or more. In addition, surface fog at a non-image portionwas not caused. Even in a long-period durability test using one millionsheets of A4-sized paper, stable characteristics were shown in whichchanges in the charge amount and the image density tended not to occur.Furthermore, the uniformity was excellent when a whole-surface solidimage was developed. A development memory was not generated. Thetransfer efficiency was 90% or more. In addition, stable characteristicswere shown in which the charge amount tended not to decrease at hightemperature or high humidity, and in which the charge amount did nottend to change at low temperature or low humidity.

However, when an image was developed by using the developing agent d6, acharge-up was drastic, and the charge amount increased, so that theimage density was extremely reduced.

Furthermore, when an image was developed by using the developing agentsd7 to d11, fusion of toner to the carrier tended to occur, carrierresistance changed significantly, the charge amount tended to decrease,and fog tended to increase. The charge amount decreased at hightemperature or high humidity, so that fog increased. The charge amountincreased at low temperature or low humidity, so that the image densitywas reduced. The transfer efficiency was decreased to approximately 60%.

INDUSTRIAL APPLICABILITY

The present invention provides a carrier for electrophotography having ahigh durability and a long lifetime, in which the charge amount does notdecrease at high temperature or high humidity nor extremely increase atlow temperature or low humidity, in which a deterioration of adeveloping agent caused by stripping of a coating layer is prevented,and in which a deterioration caused by formation of spent toner of atoner is also prevented, by coating a surface of a core material with acoating resin containing a fluorine modified silicone resin and anaminosilane coupling agent as described above.

1. A carrier for electrophotography in which a surface of at least acore material is coated with a resin, wherein the coating resin containsa fluorine modified silicone resin and an aminosilane coupling agent,wherein the aminosilane coupling agent is included in a range of 5 to 40weight parts with respect to 100 weight parts of the coating resin, andwherein the carrier charges a toner negatively.
 2. The carrier forelectrophotography according to claim 1, wherein the resin coating layerfurther comprises conductive microparticles within a range of 1 to 15weight parts with respect to 100 weight parts of the coating resin. 3.(canceled)
 4. The carrier for electrophotography according to claim 1,wherein the proportion of the coating resin is within a range of 0.1 to5.0 weight parts with respect to 100 weight parts of the carrier corematerial.
 5. The carrier for electrophotography according to claim 1,wherein a releasing agent wax is further added to the toner within arange of 4 to 20 weight parts with respect to 100 weight parts of abinding resin of the toner.
 6. The carrier for electrophotographyaccording to claim 1, wherein inorganic microparticles with an averageparticle size of 6 to 120 nm that has been subjected to a hydrophobictreatment are adhered on a surface of the toner within a range of 0.5 to4.5 weight parts with respect to 100 weight parts of the toner.
 7. Thecarrier for electrophotography according to claim, wherein the fluorinemodified silicone resin is a crosslinked fluorine modified siliconeresin obtained by reacting polyorganosiloxane and an organic siliconcompound containing a perfluoro alkyl group.
 8. The carrier forelectrophotography according to claim 7, wherein the organic siliconcompound containing a perfluoro alkyl group is at least one compoundselected from CF₃CH₂CH₂Si(OCH₃)₃, C₄F₉CH₂CH₂Si(CH₃)(OCH₃)₂,C₈F₁₇CH₂CH₂Si(OCH₃)₃, C₈F₁₇CH₂CH₂Si(OC₂H₅)₃, and(CF₃)₂CF(CF₂)₈CH₂CH₂Si(OCH₃)₃.
 9. The carrier for electrophotographyaccording to claim 7, wherein the polyorganosiloxane is at least oneselected from Chemical Formulas 1 and 2 below:

where R¹ and R² denote a hydrogen atom, a halogen atom, a hydroxy group,a methoxy group, or a C1 to C4 alkyl group or phenyl group, R³ and R⁴denote a C1 to C4 alkyl group or phenyl group, and m denotes an averagepolymerization degree and is a positive integer,

where R¹ and R² denote a hydrogen atom, a halogen atom, a hydroxy group,a methoxy group, or a C1 to C4 alkyl group or phenyl group, R³, R⁴, R⁵and R⁶ denote a C1 to C4 alkyl group or phenyl group, and n denotes anaverage polymerization degree and is a positive integer.
 10. The carrierfor electrophotography according to claim 7, wherein the fluorinemodified silicone resin is a crosslinked fluorine modified siliconeresin obtained by reacting an organic silicon compound containing aperfluoro alkyl group with polyorganosiloxane within a range of 3 to 20weight parts with respect to 100 weight parts of the polyorganosiloxane.11. The carrier for electrophotography according to claim 1, wherein theaminosilane coupling agent is at least one selected fromγ-(2-aminoethyl)aminopropyltrimethoxysilane,γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, andoctadecylmethyl[3-(trimethoxysilyl)propyl]ammonium chloride.